The present invention relates to an antenna feed and, more particularly, to an antenna feed adapted for simultaneous transmission, reception and tracking in multiple designated frequency bands of the telemetry spectrum.
The telemetry spectrum is required for transmission of real time data from a test vehicle to ground. The traditional telemetry frequency bands, located between 1400 to 2400 MHz, are extensively used for both commercial and military flight-testing activities. Additional frequency spectrum allocations for aeronautical mobile telemetry, for flight-testing are located in the C-band (4400 to 6700 MHz).
Antennas available for telemetry, employing multiple frequency bands for communication, require interchangeable separate feeds for transmission and/or reception of each of the frequency bands in use. Changing a frequency band, supported by a prior art antenna for data transmission or reception, requires a physical removal of the antenna feed from the reflector focal point and a physical installation of a new antenna feed and associated RF equipment, that support the new frequency band, into the focal point of the reflector. This installation procedure is a time consuming process and may result in misalignment of the reflector and antenna feed causing distorted antenna radiation patterns.
Antennas with separate feeds, each operating in a single frequency band, can be used in conjunction with a dichroic sub reflector, wherein one feed is located at the main reflector focus and a second feed is located at the sub reflector focus. Current telemetry tri-band solutions utilize an LIS-band feed at the main reflector's focal point and a C-band feed at the sub-reflector's focal point. This configuration tends to be inherently narrow band. Furthermore, the sub reflector blocks part of the antenna radiation, especially in mobile antennas with small main reflectors. Imperfections of the dichroic material also result in gain reduction due to some attenuation of the signal at the wavelengths where the signal should pass unattenuated through the material and some transmission through the material at those wavelengths for which the material has to be a perfect reflector. This configuration also requires sub reflector redesign, as to match each main reflector specified for use.
U.S. Pat. No. 4,041,499 describes a direction finding (DF) coaxial antenna that supports at least two frequency bands. The DF antenna of U.S. Pat. No. 4,041,499 is not configured for receive, transmit and tracking of telemetry applications and thus is not required to be coupled to a reflector that poses limitations on the feed dimensions.
It would be highly advantageous to have a single compact feed for efficient and simultaneous reception, transmission and tracking in multiple frequency bands, in conjunction with a reflector. It would be also highly advantageous to have a method for a modular and easy installation and upgrade of a telemetry ground antenna, by replacing an existing feed, with a single multi band feed that supports more or other frequency bands in addition to the currently employed frequency band(s).